A rocket ship 102 is a rocket-propelled spaceship, which is a vehicle used for space travel or space missions 104. Today, the U.S. space program is limited to short trips to planets that are within proximity to Earth, such as Mars. The National Aeronautics and Space Administration has expressed a desire to accomplish deeper space missions, such as to Jupiter and beyond. As a result, the time that the rocket ship 102 would have to spend in space would have to grow correspondingly longer. Rockets that are used for short trips are inadequate to last for the duration of deep space missions. For these missions, rockets may have to last up to 5-10 years or longer. That is an order of magnitude longer than most rockets that are designed for today's usage. Various efforts are underway to identify life-limiting factors of rockets. One of the life limiting factors is the erosion of the exhaust nozzles (grids) of rockets. This and other problems are more fully illustrated below.
A rocket 100 is a jet engine that operates on the same principle as a piece of fireworks that a child may detonate on the Fourth of July. The rocket 100, which consists of a combustion chamber 106 and exhaust nozzles or grids 108, 110, carries liquid, solid, or plasma propellants that provide the fuel needed for propulsion and thus make the engine independent of the need for oxygen from the Earth's atmosphere, facilitating the rocket's use for space missions 104. If the rocket 100 is an electric rocket, it accelerates and expels charged particles through grids 108, 110 to thrust forward in the direction 112 while charged particles move in an opposite direction 114.
Plasma rockets are a type of electric rocket that uses a powerful electrical current to energize a gas within the combustion chamber 106 to turn it into a plasma. Plasma is a state of matter in which atoms have been ionized by electrical current. A collection of charged particles (including ions, free electrons, and neutral atoms with equal numbers of positive ions and electrons and exhibiting some properties of the former gas) is a good conductor of electricity and can be influenced by an electromagnetic field. A conventional type of plasma rocket uses a screen grid 108 that is proximally located to the combustion chamber 106. Distally located from the combustion chamber 106 is an accelerator grid 110. A strong electrical field is placed between the screen grid 108 and the accelerator grid 110, which acts to attract charged particles, such as ions, to the screen grid 108 and accelerates the charged particles out from the combustion chamber 106 through the accelerator grid 110 in the direction 114, hence propelling the rocket 100 toward the direction 112.
Grids 108, 110 are large plates that have numerous holes in them allowing charged particles to move through them. Typically, the screen grid 108 is made electrically positive (from one to several thousand volts) and the accelerator grid is made electrically negative (from one to several hundred volts). The potential difference between the two grids 108, 110 attracts and accelerates charged particles out and away from the combustion chamber 106. As the charged particles emerge, a small number of them may be attracted to the accelerator grid 110 and collide with the accelerator grid 110. In addition, some of the charged particles that exit the plasma rocket may experience a charge-exchange collision. These collisions result in charged particle being created with a low initial energy. This low energy initial condition inhibits newly created charged particles from having enough kinetic energy to overcome the potential gradients created by the accelerator grid 110 and a significant portion of these charged particles are accelerated toward the accelerator grid 110. These collisions between charged particles and the accelerator grid cause material to be ejected from the accelerator grid and are referred to as sputtering of the accelerator grid 110 and over time may cause significant deterioration of the accelerator grid 110.
Another problem that tends to deteriorate the accelerator grid 110 is arcing between the two grids. Depending upon the grid materials and the amount of energy stored in the arc, arcing can create a well or a pit in the accelerator grid, which gets deepened with repeated arcings until irreversible erosion results. An active area of research is to find a substance from which to build the accelerator grid 110 that could resist collisions with charged particles, hence enhancing the resistance to sputtering. The conventional substance that is used to make the accelerator grid 110 is molybdenum. Molybdenum is easily machinable to form the accelerator grid 110. One surprising material behavior of molybdenum is its resistance to arcing in that a well is unlikely to develop even with repeated arcing. The problem with molybdenum is its vulnerability to sputtering.
One attempt to provide a more sputtering-resistant substance has led to the use of carbon in the form of both graphite and carbon-carbon composite to supplant molybdenum for manufacturing the accelerator grid 110. The problem with these forms of graphite, however, is that the manufacturing process can result in minute fiber strands on the surface of the accelerator grid 110. Given that grids 108, 110 are separated by very small distance, these graphite fiber strands may cause multiple arcings to occur. Each arcing has an energy level associated with it. If the energy level is just enough to evaporate the graphite fiber strand, no further erosion of the accelerator grid 110 is likely to occur and the arcing will diminish with time. However, if there is too much energy in the arc, it will form a well or pit that deepens with repeated arcing. The arc deposits a great amount of energy upon the graphite fiber strand creating more fiber strands that over time will cause more arcing. This repeated arcing will either cause the spacecraft control system to turn the engine off for otherwise a hole is then formed. Either way the accelerator grid 110 will be destroyed completely.
The destructive power of arcing can be controlled by limiting the amount of energy presented to the grids 108, 110 by the power supply of the rocket 100. Conventional power supplies for rockets that use plasma propellants were designed for grids that are made out of molybdenum. Conventional power supplies have too much energy to actify grids 108, 110 made from graphite. The source of the energy that causes destructive arcings is a low-pass filter component in the output stage of a conventional power supply. The purpose of the low-pass filter component of the output stage is to smooth out the output DC voltage signal from the power supply. Such a voltage signal requires a large capacitor to implement the low-pass filter component for filtering substantial portions of the DC voltage signal. This large capacitor stores a great amount of energy that is unleashed with each arcing and destroys the accelerator grid 110 over time.
As a result of the desire to explore deeper expanses of space, rocket ships need rockets that can last twice as long as conventional rockets. One factor that has limited the useful life of conventional rockets is the erosion of the accelerator grids. The use of graphite as a substance to form the accelerator grid has overcome many of the problems associated with sputtering, but graphite is susceptible to arcings. Arcings act as a medium to transfer a great amount of destructive energy stored by conventional power supplies of conventional rockets and that in turn erodes the accelerator grid. Without a solution to enhance rocket power supplies to maintain the viability of accelerator grids, it may not be possible to have deep space missions to better understand our universe. Thus, there is a need for a method and a system for enhancing rocket power supplies while avoiding or reducing the foregoing and other problems discussed above.